The presence of large amounts of genetic variability at allozyme loci in natural populations of many organisms has raised the issue of the adaptive significance of these genetic variants. The objective of this research is to characterize variation at allozyme loci in natural and experimental populations and to study the action of forces which result in the maintenance of this genetic variability. Research will utilize populations of Drosophila and center on four areas of investigation: (1) The characterization of heat-sensitive variants of electrophoretic allozyme alleles, (2) A survey of seasonal and microgeographic variability in the frequencies of enzyme genes, (3) A search for linkage disequilibria between allozyme loci, and (4) The role of frequency dependent selection in the maintenance of allozyme-gene polymorphisms. Variation at allozyme loci will be detected using the methods of starch gel electrophoresis and selective enzyme staining.